A display device in which a display unit and a touch sensor unit are combined is used. A detection region of the touch sensor unit overlaps with a display region of the display unit, so that the display device displays an image in the display region and can obtain information of the position in the display region indicated by a user. The user performs input with a finger, a stylus, or the like.
A transistor including an oxide semiconductor can be used for a pixel of the display unit. A transistor including an oxide semiconductor exhibits an extremely low off-state current; hence, the frequency of refresh operations when a still image is displayed by the display unit can be reduced. In this specification and the like, the technique for reducing the frequency of refresh operations is referred to as idling stop or IDS driving (Patent Document 1 and Patent Document 2). The IDS driving can reduce power consumption of the display unit.